Related summary of the cross-intersection method for high school chemistry calculations, and related examples.

1. Cross multiplication method

This is a method of writing chemical formulas of substances using valence. It is suitable for compounds composed of two elements or two groups. The principle it is based on is the law of valence: the algebraic sum of the total number of positive valences and the total number of negative valences is 0 or the absolute value of the total number of positive valences and the total number of negative valences is equal. 2. Cross comparison method

The cross method we often call is actually the cross comparison method, which is a graphical method. The cross diagram method is actually a simple algorithm that replaces the summation formula. It is particularly suitable for the calculation of mixtures of two total quantities and two relationships (i.e., 2-2 type mixture calculation). It is used to calculate the two components of the mixture. ratio of ingredients.

3. Cross elimination method

The cross elimination method is referred to as the cross elimination method. It is a solution to a type of ion inference problem. Using "cross elimination" can reduce the number of unknown substances. range, so that you can use the conditions given in the question to determine the substance and find the correct answer.

In fact, the cross method is a simple form of solving linear equations of two variables. If you are really not used to it, you can solve it with an example. But I still tell you. For example, the density of A is 10, and the density of B is 8. Their The density of the mixture is 9. You can put 9 in the middle, write 10 and 8 on the left, mark AB, and then subtract 9 respectively. You can get the right side to be 1 1. At this time, the ratio is 1:1. This example is relatively simple, but it is also difficult. You should experience it yourself. This method is actually very good at saving time, especially when taking comprehensive science exams

Example: A gas has a relative molecular mass of 28, and B gas has a relative molecular mass of 34. There will be no reaction after mixing. The average relative molecular mass of the gas is 30. Find the volume ratio of A`B.

Solution:

A 28 4

30

B 34 2

So V(A):V(B)=4:2=2:1

Here 2=30-28

4=34- 30